Patent GB-1321655-A (GB)
Title: Exercising device
IPC: A61B5/22
Filed: 1970-08-25
Abstract: 1321655 Exercising apparatus AMERICAN GAGE & MACHINE CO 25 Aug 1970 [5 Nov 1969] 40837/70 Heading A6M [Also in Division G3]  A control system for a generator comprises a regulator to maintain the output voltage at a substantially constant value and another regulator which is responsive to the generator frequency (and hence the speed) to vary the generator power output with variations of frequency the arrangement being such that the power losses dependent on speed are compensated to maintain constant the horsepower input to the generator. The invention is embodied in the bicycle type exercising device shown in Figure 1 to maintain constant the energy expended by the user, who pedals the wheel 6 which drives the shaft of an alternator 24 whose rectified output is supplied to a load comprising the resistors 70..82 shown in Figure 4. A switch 44 mounted on a control panel 38 enables the user to select appropriate resistors corresponding to a desired energy output. The rectified output voltage of the alternator is maintained at a desired value by a voltage regulator 34 of the type comprising a switching transistor 112 which controls the current through the field winding 50 of the alternator in accordance with the difference between the output voltage and a reference value set by a Zener diode 100. A switch 40 on the control panel 38 is closed by the user at start-up to energise the field winding 50 by a battery 117, the switch being opened, again by the user, when a lamp 42 lights up to indicate that alternator voltage is available to energise the winding 50. The regulator 34, which may be replaced by other known types, provides a constant power output which is varied by a compensating control circuit 36 arranged to respectively increase or decrease the power with decrease or increase of alternator frequency. To this end an AC signal, obtained from one of the alternator windings 48, is passed through a decoupling, currentlimiting circuit 120, 122 to a squaring circuit including a transistor 124 producing a square wave signal of the same frequency as the AC signal. The former signal is applied to a differentiating circuit 128, 130 whose output signal is also of the same frequency and is applied to an integrating circuit 134, 136, 138 the magnitude of whose output is proportional to the frequency. This output varies the conduction of a transistor 141 forming, with an adjustable resistor 142, a variable resistance circuit in parallel with the load resistors 70.. 82. Thus as the speed-dependent losses in the alternator 24 vary, the conduction of transistor 141 is varied to alter the power output and so maintain constant the horsepower input to the alternator. The following modifications may be made to the control system: (1) the squaring circuit may control a one-shot multivibrator controlling the parallel resistance circuit, which in this case is of fixed resistance and is connected in parallel with the load resistors for a period during each alternator cycle depending on the frequency, Fig. 5 (not shown). (2) the frequency-responsive signal may be used to control the regulator 34 so that the value of regulated voltage is adjusted to vary the power output. The signal is passed through a calibration circuit having a switch gauged to the switch 44 of the load circuit, Fig. 6 (not shown) (3) the frequency-responsive signal is obtained by sensing the alternator field current, the signal again being used to control the regulator 34 via a calibration circuit, Fig. 7 (not shown).